1. Field of the Invention
The present invention relates to an image processing device which processes a medical image and the like, a control method which is applied to the image processing device, and a control program which is used to execute the control method.
2. Related Background Art
Recently, the monitor diagnosis in which a medical image is used is widespread because of the advance of computer technology and the increase of memory storage capacity. More specifically, a radiographic image (X-ray image, gamma-ray image, or the like) radiographed or taken by modality (e.g., a radiation detector) is stored in a digital file, and the stored image is subjected to image processes such as a gradation transformation process, an enlargement/reduction process, an edge emphasis process and the like, whereby the processed image is displayed as the medical image on the monitor and thus used in the medical diagnosis.
Here, it should be noted that that the gradation transformation process includes a linear process and a non-linear process. That is, in the linear process, when the signal value in the image file taken by the modality is transformed into the output value to be displayed on the monitor, the range of the signal to be displayed is changed, and the contrast of the signal to be displayed is emphasized. Hereinafter, this process is called the operation of a lookup table. On the other hand, in the non-linear process, the gamma value is changed and sigmoid transformation is executed so as to approximately conform to the characteristic of the image output to a film.
Here, the operation of the lookup table will be explained with reference to FIGS. 16 and 17.
FIG. 16 is the graph showing the relation in case of transforming the value (input value) in the image file into the value (output value) to be displayed on the monitor, and FIG. 17 is the conceptual view showing a first example of the image display state in a case that the window values are changed.
Ordinarily, the dynamic range of the modality is larger than the dynamic range of the monitor. For this reason, the partial range in the digital image is often degenerated into the dynamic range of the monitor for medical image and displayed on this monitor. Here, it is assumed that the dynamic range of the image file is equivalent to 12 bits, and the dynamic range to be output to the monitor is equivalent to eight bits.
As shown in FIG. 16, the range in the input value to be used for the output value is the window width (WW), and the intermediate value of the window width is the window level (WL). Typically, as the initial value in case of first displaying the image, the window width (WW) is equivalent to the dynamic range of the modality (that is, 212=4096 in case of 12 bits). Therefore, the window level (WL) is often set to be equivalent to the half of the WW (that is, 211=2048) (1401 shown in FIG. 17). Incidentally, it is assumed that the line P shown in FIG. 16 is called the WW/WL line hereinafter.
As shown in FIG. 17, if the window level (WL) is decreased, the whole image becomes light (1402 shown in FIG. 17), and, if the window level (WL) is increased, the whole image becomes dark (1403 shown in FIG. 17). On the other hand, if the window width (WW) is increased, the whole image becomes soft by decreasing the contrast (1404 shown in FIG. 17), and, if the window width (WW) is decreased, the whole image becomes sharp (1405 shown in FIG. 17).
The document 1 (Japanese Patent Application Laid-Open No. 2002-333974) discloses the image processing device which sets the various image processing parameters including not only the window width (WW) and the window level (WL) but also the parameters to be used to execute the non-linear processes, by shifting the pointing device. In the document 1, the kind of parameter and the increase/decrease directions of the parameter value can be changed according to the designation by the user.
However, the radiographic image includes the image of which the input signal value “0” indicates white (hereinafter, called “image of monochrome 1” because its photometric interpretation value is defined as “monochrome 1” in the DICOM (Digital Imaging and Communication in Medicine) standard) and the image of which the input signal value “0” indicates black (hereinafter, called “image of monochrome 2” because its photometric interpretation value is defined as “monochrome 2” in the DICOM standard). Here, many image viewers corresponding to the DICOM standard display “image of monochrome 2” as it is and display “image of monochrome 1” in a grayscale inversion manner, whereby the input signal value “0” is displayed as black even if the photometric interpretation of the image is different.
Likewise, if the image viewers display “image of monochrome 1” as it is and display “image of monochrome 2” in a grayscale inversion manner, the input signal value “0” is displayed as white irrespective of the photometric interpretation of the image.
Here, it should be noted that whether the photometric interpretation of the medical image corresponds to “image of monochrome 1” or “image of monochrome 2” depends on the modality.
Incidentally, the plural modalities are mutually connected through the network, whereby various medical images are accumulated in the one PACS (Picture Archiving and Communication System). Thus, in the individual medical diagnosis scene, “image of monochrome 2” and “image of monochrome 1” often come to exist together.
FIG. 18 is a conceptual view showing a second example of the image display state in a case that the window values (WW, WL) of the grayscale inversed image are changed.
In case of displaying the grayscale inversed image, as indicated by numeral 1501 shown in FIG. 18, the image is acquired by up-and-down inverting the image 1401 shown in FIG. 17. For this reason, if the window level (WL) is decreased, the whole image becomes dark (1502 shown in FIG. 18). Moreover, if the window level (WL) is increased, the whole image becomes light (1503 shown in FIG. 18). Incidentally, as well as “image of monochrome 2”, if the window width (WW) is increased, the whole image becomes soft by decreasing the contrast (1505 shown in FIG. 18), and, if the window width (WW) is decreased, the whole image becomes sharp (1504 shown in FIG. 18).
That is, in the ordinary display of “image of monochrome 2” and the ordinary display of “image of monochrome 1”, as shown in FIG. 17, if the window width (WW) is fixed and the window level (WL) is decreased, the whole image becomes light, while if the window level (WL) is increased, the whole image becomes dark. On the contrary, in the grayscale inversed display of “image of monochrome 1” and the grayscale inversed display of “image of monochrome 2”, as shown in FIG. 18, if the window width (WW) is fixed and the window level (WL) is decreased, the whole image becomes dark, while if the window level (WL) is increased, the whole image becomes light.
However, as described above, to display just the same the images of which the photometric interpretations are respectively different from each other, it is necessary to display one of these images in the grayscale inversion manner. That is, to display the input signal value “0” as black irrespective of the photometric interpretation of the image, “image of monochrome 2” is displayed ordinarily and “image of monochrome 1” is displayed in the grayscale inversion manner. Moreover, to display the input signal value “0” as white irrespective of the photometric interpretation of the image, “image of monochrome 2” is displayed in the grayscale inversion manner and “image of monochrome 1” is displayed ordinarily. For these reasons, even in a case where the appearances of the images to be displayed on the monitor are the same, if the window level (WL) of the image displayed ordinarily and the window level (WL) of the image displayed in the grayscale inversion manner are changed in the same manner, there is a problem that the brightness (lightness and darkness) of one image acquired in the image process becomes opposite to that of the other image. More specifically, the brightness of the image displayed ordinarily becomes opposite to the brightness of the image displayed in the grayscale inversion manner.
Therefore, in the case where a diagnostician who has plural modalities respectively having the different photometric interpretations changes the window level (WL) of the medical image, it is necessary for him/her to be conscious of the photometric interpretation of the image to which he/her intends to diagnose. For this reason, the diagnostician has to discriminatingly use the operation according to the photometric interpretation.